12. symlinks

When you list files in detail, you see a lot of information. Let's look at a previous example of inode information from the ls -li command:

pete@icebox:~$ ls -li
140 drwxr-xr-x 2 pete pete 6 Jan 20 20:13 Desktop
141 drwxr-xr-x 2 pete pete 6 Jan 20 20:01 Documents

We've previously glossed over the third field in this output. This field is the link count.

The Link Count in Linux

The link count in linux is the total number of hard links a file has. To understand what this means, we first need to discuss what links are. In Linux, there are two types of links: symbolic links (symlinks) and hard links.

Understanding Symlinks

In the Windows operating system, you have shortcuts, which are essentially aliases that point to other files. In Linux, the equivalent is a symbolic link, also known as a soft link or symlink. A symlink is a special type of file that points to another file or directory by its name.

Let's see this in practice. We'll create a few files and then a symlink.

pete@icebox:~/Desktop$ echo 'myfile' > myfile
pete@icebox:~/Desktop$ echo 'myfile2' > myfile2
pete@icebox:~/Desktop$ echo 'myfile3' > myfile3

pete@icebox:~/Desktop$ ln -s myfile myfilelink
pete@icebox:~/Desktop$ ls -li
total 12
  151 -rw-rw-r-- 1 pete pete 7 Jan 21 21:36 myfile
93401 -rw-rw-r-- 1 pete pete 8 Jan 21 21:36 myfile2
93402 -rw-rw-r-- 1 pete pete 8 Jan 21 21:36 myfile3
93403 lrwxrwxrwx 1 pete pete 6 Jan 21 21:39 myfilelink -> myfile

Here, we've created a symbolic link named myfilelink that points to myfile. When you use ls to view an ls symlink, it's clearly identified by the l at the beginning of the permissions string and the -> symbol pointing to the target. Notice that the symlink has its own unique inode number (93403). Because symlinks point to filenames rather than inodes, they can span across different filesystems.

Understanding Hard Links

The other type of link is a hard link. A hard link creates another file entry that points directly to the same inode as the original file.

Let's create a hard link for myfile2:

pete@icebox:~/Desktop$ ln myfile2 myhardlink
pete@icebox:~/Desktop$ ls -li
total 16
  151 -rw-rw-r-- 1 pete pete 7 Jan 21 21:36 myfile
93401 -rw-rw-r-- 2 pete pete 8 Jan 21 21:36 myfile2
93402 -rw-rw-r-- 1 pete pete 8 Jan 21 21:36 myfile3
93403 lrwxrwxrwx 1 pete pete 6 Jan 21 21:39 myfilelink -> myfile
93401 -rw-rw-r-- 2 pete pete 8 Jan 21 21:36 myhardlink

Notice that myhardlink shares the exact same inode number (93401) as myfile2. The link count for both files has also increased to 2. This is because two file entries now point to the same inode. If you modify the contents of myfile2, the changes will be reflected in myhardlink, and vice versa. If you delete myfile2, the file's data will still be accessible through myhardlink. The inode and its data are only removed from the disk when the link count drops to zero. Because hard links point to inodes, which are unique within a single filesystem, they cannot span across different filesystems.

Creating Symlinks and Hard Links

You can create both types of links using the ln command. The syntax is straightforward.

To create a symbolic link, use the -s flag:

ln -s /path/to/original /path/to/link

To create a hard link, omit the -s flag:

ln /path/to/original /path/to/link

Using ls symlinks or general ls links commands with the -l option is essential for managing and identifying these different file types.